The DFT-B3LYP method, with the basis set 6-31G, was employed to calculate the molecular geometries and electronic structures of 24 3-substituted sulfur-5-(2-hydroxyphenyl)-4H-1,2,4-triazole compounds. E_HOMO, E_LUMO, E_NHOMO, E_NLUMO, Q_C1～Q_C8, Q_N1～Q_N3, Q_O, Q_S, ΔE₁, ΔE₂, ΣQ were selected as quantum chemical descriptors (q_c). The quantitative structure-activity relationships (QSAR) were established by using leaps-and-bounds regression analysis for the antibacterial activities (A_J: A_m, A_e and A_s) of 13 compounds to Escherichia coli, Monilia albican and Staphylococcus aureus along with the q_c. The correlation coefficients (R²) and the leave-one-out (LOO) cross validation R_cv² for the A_e, A_m and A_s models were 0.930 and 0.871; 0.926 and 0.869; 0.781 and 0.572 respectively. The QSAR models have both favorable estimation stability and good prediction capability by A_adj², F, R_cv², VIF, AIC, FIT tests. The results indicate that the ΔE₁ and ΣQ are main factors which can affect the bioactivities of these compounds directly. The antibacterial activities of the compounds increase with the increase of the ΣQ; however the higher the ΔA₁ is, the lower the A_J is. The possible mechanism has been given for the antibacterial of the triazole compounds. It is known that the suitable structural modifications of R group in triazole compounds with the strong electron- attracting one are beneficial to the antibacterial activities. According to the results (11 compounds) obtained from the structural modifications, the antibacterial activities of four modified molecules are over 100% when mass fraction is 0.01%, and it is expected to be confirmed by using biologic experiments.

Key words: 3-substituted sulfur-5-(2-hydroxyphenyl)-4H-1,2,4-triazole, density functional theory (DFT), quantum chemical descriptor, Escherichia coli, Monilia albican, Staphylococcus aureus, antibacterial activity, antibacterial mechanism, quantitative structure-activity relationship (QSAR)